The complicated history of simple scientific facts

Facts we take for granted—like e=mc2—often have a long story behind them.

Sometimes, even as a person pisses you off, they make a point that you can't ignore. In a recent forum discussion that I was involved in, scientists were accused of making pronouncements from on high. The argument was that scientists jump to a conclusion that seems desirable to them, and then treat it as an infallible truth.

Of course, my initial reaction was to pronounce that I, as a practicing scientist, never make pronouncements. But, looking at my articles from the perspective of someone who really knows absolutely nothing about science—as a practice or as a body of knowledge—I can see how one could see little beyond a list of assertions. The truth is more complicated, of course, but it's a truth that science writers find challenging to convey. Science is impossibly broad, and the leading edge sits, precariously balanced, on a huge, solid, and above all, old body of knowledge. To illustrate this problem, I am going to tell you the story about how the speed of light came to be the ultimate speed limit for the entire universe.

What I want you to remember from this story is that any new fact or change in our understanding sits upon generations of accumulated knowledge. Most of that knowledge is now trusted as "mostly correct," though some of it still lies in the "probably not too badly wrong" category. Sitting beneath that is a body of work stretching back some 6,000 years, some of which is still highly relevant.

My overall point is that, even if I were to extend each of my peer-reviewed articles by some 3,000 words—I already get complaints about the length of some of my articles—I still would not have covered the science of an entire subject. By choosing a starting point for the knowledge described in an article, I really am pronouncing from on high that everything beyond that point is established, trusted knowledge, while everything after that point will be explained to some extent.

So, how do we measure stuff anyway?

My arbitrary beginning for this story—and make no mistake, it is a story that leaves out any number of complications—is Galileo. Apart from being a telescope builder extraordinaire, Galileo also had an important insight into the process of measurement. He saw that if he was on a moving boat and fired a cannon forward, he could measure the speed of the cannon ball and come up with a number. But, the poor guy on the receiving end of the cannon ball—giving up his life in the name of science—would, when making the same measurement, come up with a different answer.

Needless to say, a violent disagreement might ensue (provided the target survived the cannonball) over whose measurement was correct. Galileo saw that the difference between the two measurements was the speed of the boat. That is, the person receiving the cannon ball sees that it is moving a bit faster than Galileo because the target sees that the cannon that fired the ball was also moving. Once this extra speed is taken into account, agreement could be reached between different measurements, and Galileo could return to upsetting other people.

The key point that Galileo made clear was that measurements are always relative to some benchmark. We measure the speed of a car relative to the ground, and we measure the speed of stars relative to each other (including the Sun). This principle underlies a lot of modern physics, and it's so fundamental that we don't even give it a name when we teach it anymore.

But it turns out that this principle is, in fact, wrong sometimes. Showing how we know it's wrong and why we found out that it is wrong is what this story is really all about.

Another arbitrary beginning: the story of light

Galileo was not the only person into optics and telescopes. Newton and Huygens both made huge contributions to our understanding of light—Newton demonstrated that white light contained all the colors of the rainbow, while Huygens created a model that explained the structure of the patterns light created after it had passed by a sharp edge.

But these two giants of science disagreed about what light actually was. Newton thought that light was a particle, while Huygens thought that light was a wave. Critically, all observed phenomena could be explained by both models, so both had their adherents and critics. Note, though, that this dispute happened a bit before 1700, but this issue remained unresolved until the middle of the 19th century.

That is not to say that no one cared or did anything about it. On the contrary, evidence for the wave theory of light accumulated and the particle theory of light had to be modified to accommodate the new findings; as it became more complicated, the number of people who supported it shrunk.

The straw that broke the camel's back when it came to support for light as a particle was Young's experiment that demonstrated that light, like water waves and sound waves, could be made to interfere—one of the reasons this took so long is that Young needed a relatively modern light source to make his observations. In the meantime, an important question remained unanswered: if light was a wave, what was doing the waving?

Yet another arbitrary beginning: the story of electricity

Off in a disregarded corner, people with names like Faraday and Gauss had begun to get interested in why, after you had rubbed a cat with a bit of amber, bits of paper would stick to both the cat and the amber, but not to each other. Equally interesting was why compass needles pointed north. Although these phenomena had been known for a long long time, no one had really investigated them—or if they had, their findings had been lost. In any case, scientists got interested in static electricity and magnetism.

They discovered that some materials conducted electricity, that magnets could cause an electric current to flow, and that currents could be used to create magnets. The two were linked, but no one really knew how. Empirical laws were derived that allowed electricity and magnetism to be exploited—dynamos, electric motors, and alternators were all in the process of revolutionizing life, though their effects would take a while to percolate through society. But, despite the applications, the underlying principles remained obscure—we had laws, but no theory.

There were two problems with the laws developed for electricity and magnetism: first, they didn't shed any light on what electricity or magnetism were or why they were linked—the concept of charge had been introduced, but no one knew what a charge might be. Second, they weren't predictive: that is, whenever anyone found a new magnetic or electrical phenomena, a new law was required.

That's where things stood until the late 19th century, when Maxwell decided to use some new-fangled math to describe electricity and magnetism. He found a common set of equations that described both phenomena and how they were linked to each other.

Maxwell's work didn't win instant acceptance. In the first place, it didn't do anything about the first problem—Maxwell's equations offer no insight into the origin of electricity or magnetism, beyond the charge concept, anyway. Meanwhile, there were other theories floating around that were purely mechanistic—they solved the first problem, but failed to be predictive (or at least, accurately predictive). In addition, Maxwell's work introduced a series of new problems.

Chris Lee
Chris writes for Ars Technica's science section. A physicist by day and science writer by night, he specializes in quantum physics and optics. He lives and works in Eindhoven, the Netherlands. Emailchris.lee@arstechnica.com//Twitter@exMamaku

As you can see, an explanation for why scientists accept a particular statement can involve a story that spans several hundred years and is almost never simple.

Then it stands to reason that even with all of the scientific knowledge that we have gained so far, the application and distillation of all of that knowledge, coupled with the current research still leaves us with at least another century before we have the same level of understanding of climatic systems as we do with electricity and light. And, you're right, it's never simple.

It's an interesting article about the speed of light, but it seemed, from your introductory paragraphs, that your article was about how scientists seem to just make pronouncements when in fact they're making carefully reasoned arguments based on experimental data. Unfortunately, in your effort to demonstrate a scientific fact without pronouncement, you fall into the very trap you're clawing at:

quote:

Originally posted by Chris Lee:He found that getting observers to explain why they disagreed with each other—and, therefore, perform mathematical operations that would obtain agreement—required giving up any notion of an absolute reference frame. As if that weren't confusing enough, a constant speed of light implied that time and space were somewhat interchangeable, and that energy and mass were two sides of the same coin.

Interestingly, as an object sped up, it observed time to pass more slowly. More importantly, if you extrapolated backwards, all objects had a rest mass, which was the minimum amount of mass it could have. Finally, and most important for this story, an object with a non-zero rest mass required an infinite amount of energy to get to a speed greater than that of light.

Don't get me wrong: I'm not trying to say that this is wrong or trying to undermine your conclusion about the speed of light. Rather, it undermines your effort to show science as something other than pronouncement. Much of these two paragraphs is absolute pronouncement with no reference at all, throwing in entirely new unfamiliar terms and reaching conclusions that aren't at all self-evident.

Granted, brevity is a necessity and explaining this in any reasonable depth might require an entire book, but it does illustrate the problem with bringing science to the masses: when a scientist suddenly whips out some wild statements, attribute them to some prophetic figure, and preach them like rock-hard fact, it's easy to draw similar conclusions with religious pronouncement.

The reality the complexity of science does raise the interesting issue of whether or not we (as a society) should try to teach all the fundamentals of science to everyone, or merely bundle up the important bits and preach them as nice parables, much as religions have done before for their mythology. There are far too many similarities between a congregation nodding obediently as a preacher tells them what to believe about God and a classroom nodding obediently as a teacher tells them what to believe about Science. Maybe scientists shouldn't be opposed to the notion of science being the new religion, imparted as assumed fact for the masses with the exclusive few "in the know" actually researching and understanding the basis for the pronouncements.

If nothing else, it would be a more efficient route to an overall increase of scientific familiarity among the masses.

While this is a great read, I can't help but feel that scientists of late have failed to live up to the aura that this article creates around them. Politics, greed, ignorance, and psuedo-science certainly flourished in the past as well, but our scientists today seem more tainted than past scientist-heros.

If this is not an acute modern failing, then I suppose it could simply be that it is easy to cherry pick the history of science in a way that ignores the worst vices of humanity so that we can hold up an idealized notion of what science should be. I guess I'm okay with that.

Great job! I think it's important to emphasize to laypeople that the old-fashioned "and then you falsify or prove the hypothesis!" version of science isn't accurate: science is a product of a lot of smart people doing what they can to empirically create rational explanations for how the world works. Sometimes they proceed with incomplete and uncontrolled evidence, like in paleontology, so the standards of something becoming "accepted fact" have to vary.

However, the general idea, that we're taking an empirical approach to creating rational explanations for how the world works, remains constant, and is the heart of science.

Also kudos on not mentioning Thomas Kuhn. Kuhn did a good job of breaking scientific epistemology out of the overly rigid and logic-obsessed ideas of the early 20th centry (I'm looking at you, logical positivism!). However, Kuhn had one fatal flaw: he didn't believe in reality. Yeah, that reality, external reality, reality qua reality. Kuhn didn't believe in reality. That's what happens when you publish books in the '60's, I guess, but it's led to a lot of BS in academia and thus beyond. But combining Kuhnian ideas with a belief in reality basically "solves" the broad epistemology of science, in my view. I.e. it's the "paradigm," and the rest is "normal," erm, epistemology.

Scientists of the past were absurdly racist, and pseudoscience has always flourished. You could say it even predates the real thing. Today's people with degrees getting bought and producing "science" are a lot tamer than, say, the Tuskegee experiments, which were done by real scientists.

Nice article. But like I said in a previous post, sound has similarities that are not entirely followed through with. That is to say, sound travels at a constant speed, regardless of the movement of the object. You can travel 100km/h and the sound that you make will remain the same. If you travel at 1,000km/h, you can shout to the guy in front of you and he'll never hear you. But, if you put yourselves in a cabin, say like in an air plane, he'll hear you just fine. If you could somehow 'see' the sound wave from the ground (stationary position, naturally), you would see it travel at +/- the speed of sound + 1,000km/h. I suspect that light would do the same. Although, I'm not entirely sure what substance causes the wave pattern in light, whereas we know that air causes the wave, or bubble as I read recently it being described as, in sound. We all know that light will behave differently, and travel more slowly, in water as it does in a vacuum. Nonetheless, were a cabin capable constructed and the speed of the light measured, I'm certain we'd see the same effect we do with sound as we do with light.

I doubt if the book is closed on the debate. Or, if it is closed, certainly, barring the catastrophic destruction of mankind, it will be opened once more.

Great article. However, I am surprised to see no mention of Karl Popper in such a discussion. Anyone who has read Popper uses the word 'fact' very hesitantly, if at all. He does defend the use of what he calls dogma. He says that once you have formulated an argument or an idea it is important to defend it to the hilt. Why? Because you owe it to the world of ideas to test it to the extreme.

Nice article. Always interesting to get a new POV on the story - you definitely taught me a thing or two I was not yet familiar with.

I do have a couple of particulars I'd like to respond to, though.

quote:

This principle underlies a lot of modern physics, and it's so fundamental that we don't even give it a name when we teach it anymore.

Well, not everybody gives it a name, but some do. I recall it being referred to as Galilean relativity when I was an undergrad, not that I'm sure whether Galileo would have called it that. I didn't run into the Galilean group until I was a grad student, though.

quote:

Off in a disregarded corner, people with names like Faraday and Gauss...

And Ben Franklin. Gotta mention Ben Franklin so that the Americans in the audience don't think it was all the British, French and Germans.

quote:

Interestingly, as an object sped up, it observed time to pass more slowly. More importantly, if you extrapolated backwards, all objects had a rest mass, which was the minimum amount of mass it could have. Finally, and most important for this story, an object with a non-zero rest mass required an infinite amount of energy to get to a speed greater than that of light.

Ok, sentence two is a non sequiter from sentence one. What's more, it tickles one of my pet peeves - the concept of "relativistic mass." I believe that the most common usage when physicists talk about this stuff is to use "rest mass" = "mass." I think this is a good convention to use because the whole "relativistic mass" of a particle is only different from it's energy content by a conversion factor, re-blurring the distinction between the "mass" and "energy" of a particle.

quote:

"nothing in normal space can go faster than light, but if you can do funny things to space, you can go faster than light."

Is this related to that whole cosmological observer receding faster than the speed of light in certain metrics thing?

@wordsworm: No. You need to go back to the beginning and work it all out again. No offense intended... but you have the wrong end of the stick.

@Chris Lee -- very nice exposition. I always did like that story.

The reason that pronouncements are the only way science can be communicated is that science consists of a series of trusted pronouncements. In the end, all of that teetering edifice of knowledge and pesudoknowledge and theory holds together ONLY because the sciences are (usually) fairly draconian about weeding out the careless, the malign, and the biased. If we can't trust the practitioner, it doesn't matter how right the result is.

Training in the sciences is, really, the process of instilling these same values, convincing the student to trust those who have gone before by forcing them to attempt the same logical leaps under controlled circumstances, and weeding out those who are, for whatever reason, incapable of the same rigor.

It all comes down to confidence, to trust. The things we have mostly work. The measurements we make are mostly valid. We have blind spots and incorrect received wisdom to battle, but it's by no means hopeless. We're a long way from being even slightly justified in cockiness, however.

The sciences have their own inherent limitations, for the same reasons that make them great. It's important that when the rigors of science prevent a valid conclusion, the conclusion not be drawn. It doesn't matter how smart someone is -- when confronted with insufficient data, a good scientist merely describes a limit and goes in search of more data. I leave it to the reader to apply this idea to their favorite scientific overreach.

Originally posted by wordsworm:Nice article. But like I said in a previous post, sound has similarities that are not entirely followed through with. That is to say, sound travels at a constant speed, regardless of the movement of the object. You can travel 100km/h and the sound that you make will remain the same. If you travel at 1,000km/h, you can shout to the guy in front of you and he'll never hear you. But, if you put yourselves in a cabin, say like in an air plane, he'll hear you just fine. If you could somehow 'see' the sound wave from the ground (stationary position, naturally), you would see it travel at +/- the speed of sound + 1,000km/h. I suspect that light would do the same. Although, I'm not entirely sure what substance causes the wave pattern in light, whereas we know that air causes the wave, or bubble as I read recently it being described as, in sound. We all know that light will behave differently, and travel more slowly, in water as it does in a vacuum. Nonetheless, were a cabin capable constructed and the speed of the light measured, I'm certain we'd see the same effect we do with sound as we do with light.

I doubt if the book is closed on the debate. Or, if it is closed, certainly, barring the catastrophic destruction of mankind, it will be opened once more.

This comment was edited by wordsworm on December 01, 2009 07:35

Already been observed. Nuclear reactors have a blue glow in the water around them from charged particles that are exceeding the speed of light in that medium. It's called Cherenkov radiation. The whole "cannot travel faster than the speed of light" thing actually comes down to a question of causality. Think of it this way - if there is an absolute frame of reference against which all things are measured, like Newton thought, then great, things are easy. Things would even be easy if they worked the way Galileo thought and we had an absolute timeline (quantum gravity would have been solved eons ago). Trouble is, not only do we have the mathematics of electricity and magnetism, and many failed experiments to look for that absolute rest frame, but we also have direct evidence that there is no such thing as absolute time. Consider, for example, the lowly muon (looks almost exactly like an electron, only about 200X heavier). Now, if you produce a muon, and stare it, you'll find that it quickly falls apart. If you do it a few hundred times or more, and average the amount of time it takes them to fall apart, you'll find that it takes 2.2 microseconds (to the nearest tenth of a microsecond). But wait! There are actually muons raining down from the sky from when energetic particles hit the upper atmosphere. If you look at how long it takes them to decay by measuring their speed and figuring out where they're produced, you'll find that on average they take considerably longer (about a factor of 10), on average. The known only way to explain it is if we are observing their time to be slowed down relative to ours (and they view us as length contracted). It gets worse, though. The cosmic ray muon thing has been known since at least the 20s or 30s (details). We've gotten so good at keeping time that we've measured the effect directly by putting atomic clocks on airplanes. Even better, it turns out that the only way for GPS to work as accurately as it does is for it to not only use special relativity, but general relativity as well (interesting tidbit - when they were first making the GPS system they made it so you could turn general relativity considerations on or off because someone [not sure if it was brass or engineers or what] just didn't buy the whole GR thing; lo and behold, it would be off by, IIRC, a few more meters if they didn't take GR into account).

So, we are pretty much 100% sure that absolute time is out the window. Without some kind of absolute time to keep the past an the future separate you run the risk of losing the concept of causality (ie a chain of events that fall in a particular order where one follows from the other). No problem, Einstein says, since no energy or signal can go faster than the speed of light the order of events seen by any physical observer will be fixed and all of the cases where the order of events are ambiguous don't matter because they cannot be causally connected. Granted, there are attempts by some of the more imaginative in the physics community to figure out a consistent way to handle a universe without that requirement, but one thing they can't get away from is explaining how an apparent causality emerges in the everyday world we experience, and so far as I know none have succeeded convincingly.

So, long story short, the whole "nothing faster than the speed of light" thing is actually nothing all that special about light, per se, but about how the universe itself is logically organized in a consistent way with experimental observations and, admittedly, what is presently conceivable (don't ask me to seriously ponder the imponderable - it's more of a Zen riddle than a serious question). It just so happens that the photon was the first observed massless particle, and all massless particles must move at c. Even if they photon weren't massless, and we're only certain that it's mass is less than about 10^(-22) of an electron, we would have figured this fact out eventually as we started to see the energy and momentum of particles deviating from their Newtonian values as they do quite dramatically. In fact, the protons they use in the LHC can be treated to a decent approximation as massless (the kinetic energy of the proton is right now about 1000 greater than its rest mass energy).

Great story. I always like hearing the histories, even when it's a subject I'm already familiar with. It's often a new way to look at the events.

Regarding this "pronouncement on high" problem... it IS something that scientists get caught in, usually through no fault of their own. Researchers could use a bit better Public Relations; the current de facto method usually leaves journalists and other such people outside the field as the common interface between scientists and the public.

Obviously, the solution is better education in general, but right now I'd settle for more people like Burke and Sagan. In this age of sound-bites, TV, and low attention spans, having scientists make strong efforts to explain things in the modern, popular styles that people might actually see is vital.

Originally posted by wordsworm:Nice article. But like I said in a previous post, sound has similarities that are not entirely followed through with. That is to say, sound travels at a constant speed, regardless of the movement of the object. You can travel 100km/h and the sound that you make will remain the same. If you travel at 1,000km/h, you can shout to the guy in front of you and he'll never hear you. But, if you put yourselves in a cabin, say like in an air plane, he'll hear you just fine. If you could somehow 'see' the sound wave from the ground (stationary position, naturally), you would see it travel at +/- the speed of sound + 1,000km/h. I suspect that light would do the same....

You've missed the point of special relativity. Sound travels at a constant speed, relative to the medium it's traveling in. So, if you're moving +100km/h relative to the air, you'll measure the speed of the sound you produce as ~600km/h (and ~800km/h behind you).

This is not the way light behaves. If you're moving through space at 280,000 km/s and shine a beam of light ahead of you, you'll measure it moving at ~300,000 km/s. Similarly if you shine a beam of light behind you, you'll measure it moving at ~300,000 km/s. Also, if there's another ship traveling towards you, also going at 280,000 km/s, you'll measure the speed of their beam of light as ~300,000 km/s.

Furthermore, the time-dilation & contraction underlying these strange phenomena are measurable properties of the universe. We've measured them, and (as mentioned previously) the GPS system wouldn't work properly if we hadn't taken these effects into consideration.

It's very different to sound. With sound, you measure different speeds depending on your motion relative to the medium. With light, you always measure the same speed, no matter how you're moving.

I'll take you back to the original question, which I think I've answered though I'll not get too much into it, which was, "Do we orbit around the sun or the image of the sun?"

Well, first to explain the question: the sun travels through the galaxy at a significant speed. What we see, when we look at the sun, is not the sun itself, but rather a phantom, or image, of the sun as it was 8 minutes ago. If it were to go super nova, we wouldn't even know about it until 8 minutes later (assuming we could see it and not be obliterated.)

The physics professor, who used to teach the class in the same auditorium as one of my English professors, said to me that there's this scientific guesstimate that gravity travels at the speed of light. I pressed on and asked him if there was any proof. He said that there wasn't.

So, I must say, I pondered this question for quite some time. A bit more than a year to be exact. I guess it was when I was reading Plato's dialogues when I ran into the statement that what we see is but an inferior form of the form itself. He was talking about literature (or Socrates anyways), but it made me think that maybe what we see and what is reality are two completely different things.

With this in mind, I started mapping out or drawing out figures which represented phantoms of stars around which a given object was orbiting and plotted the course around the star. I then came to the realization that the phantom image that we see would actually change as the orbiting object intersected the trajectory of the orbited object the phantom image would actually change. That is to say, as you cross its future path, the phantom image would actually become closer to the actual object. The exact opposite would be true as the orbiting object crossed the trail of the orbited object. The phantom image would be at its furthest point away from the actual object.

This led me to further questions about regarding the differential of the gravitational pull between the apogee position and the perigee position at these differing positions. I couldn't really answer that question. I tried to play around with differing speeds of orbited object until I got to any orbited neutron which has an orbiting electron. If that atom moved at even half the speed of light, it would render any orbit at all impossible if gravitational effect moved merely at the speed of light. It was then that I realized that gravity, or the effect of gravity was instantaneous rather than at the speed of light as the professor had suggested. I also realized a number of other things by continuing with the logic, but I'd be surprised if you're interested in hearing more.

I didn't miss the point of special relativity. I was disagreeing with it. And a sound wave doesn't change speed according to the object making the sound. It remains constant no matter how you're moving. If, on the other hand, the medium itself is moving, as in the air in the cabin of an airplane, it changes everything.

GPS systems need constant corrections in order for them to function. If we'd absolutely figured all this stuff out we'd not have to do that. That is to say, since we have the calculations for them to remain above in the starry heaven, then why do they need constant corrections? No, that's not the case. The calculations you see are averages, not constants.

I am not claiming to know all the answers. Einstein wasn't expected to get everything right. Hell, if we did, then we wouldn't have the Big Bang, now would we?

Originally posted by wordsworm:GPS systems need constant corrections in order for them to function. If we'd absolutely figured all this stuff out we'd not have to do that. That is to say, since we have the calculations for them to remain above in the starry heaven, then why do they need constant corrections? No, that's not the case. The calculations you see are averages, not constants.

That's probably because light travels slower through the air. The "speed of light" is only the speed of light in a vacuum.

There has been experimental confirmation that to a high degree of precision, gravity propogates at <em>c</em>.

I don't understand your comment about the orbits of electrons around nuclei, though. Even if we throw quantum mechanics out, I <em>think</em> you might be saying that if V_{part} > .5 c, a circular orbit for an electron would be unable to "catch up" to the bulk motion of the nucleus. Disregarding the problematic model, though, you need to consider relativistic addition of velocities and the fact that to all particles involved, signals are being transferred at <em>c</em> in all reference frames, so it still works out OK.

<sloppy>In reality, the probability distribution of the electron is localized on the nucleus, and the electron as a particle isn't *really* localized with a well-defined orbit.</sloppy>

Consider, for example, the lowly muon (looks almost exactly like an electron, only about 200X heavier). Now, if you produce a muon, and stare it, you'll find that it quickly falls apart. If you do it a few hundred times or more, and average the amount of time it takes them to fall apart, you'll find that it takes 2.2 microseconds (to the nearest tenth of a microsecond). But wait! There are actually muons raining down from the sky from when energetic particles hit the upper atmosphere. If you look at how long it takes them to decay by measuring their speed and figuring out where they're produced, you'll find that on average they take considerably longer (about a factor of 10), on average. The known only way to explain it is if we are observing their time to be slowed down relative to ours (and they view us as length contracted). It gets worse, though. The cosmic ray muon thing has been known since at least the 20s or 30s (details). We've gotten so good at keeping time that we've measured the effect directly by putting atomic clocks on airplanes. Even better, it turns out that the only way for GPS to work as accurately as it does is for it to not only use special relativity, but general relativity as well (interesting tidbit - when they were first making the GPS system they made it so you could turn general relativity considerations on or off because someone [not sure if it was brass or engineers or what] just didn't buy the whole GR thing; lo and behold, it would be off by, IIRC, a few more meters if they didn't take GR into account).

So, we are pretty much 100% sure that absolute time is out the window. Without some kind of absolute time to keep the past an the future separate you run the risk of losing the concept of causality (ie a chain of events that fall in a particular order where one follows from the other). No problem, Einstein says, since no energy or signal can go faster than the speed of light the order of events seen by any physical observer will be fixed and all of the cases where the order of events are ambiguous don't matter because they cannot be causally connected. Granted, there are attempts by some of the more imaginative in the physics community to figure out a consistent way to handle a universe without that requirement, but one thing they can't get away from is explaining how an apparent causality emerges in the everyday world we experience, and so far as I know none have succeeded convincingly.

There has been experimental confirmation that to a high degree of precision, gravity propogates at <em>c</em>.

I don't understand your comment about the orbits of electrons around nuclei, though. Even if we throw quantum mechanics out, I <em>think</em> you might be saying that if V_{part} > .5 c, a circular orbit for an electron would be unable to "catch up" to the bulk motion of the nucleus. Disregarding the problematic model, though, you need to consider relativistic addition of velocities and the fact that to all particles involved, signals are being transferred at <em>c</em> in all reference frames, so it still works out OK.

<sloppy>In reality, the probability distribution of the electron is localized on the nucleus, and the electron as a particle isn't *really* localized with a well-defined orbit.</sloppy>

The problem with that observation, Tiger, is that it uses light to measure gravity. As is said in the article, what may have been measured was the speed of light, not the speed of gravity itself. I'm curious, do you then believe that the earth is attracted to the image of the sun rather than the sun?

Originally posted by Soulrift:There are far too many similarities between a congregation nodding obediently as a preacher tells them what to believe about God and a classroom nodding obediently as a teacher tells them what to believe about Science.

Fortunately, the classroom students are (potentially if the teacher/school system allows) able to put the science teachings to the test in the form of experiments and see for themselves if what is being said is true.

Unfortunately for the priests congregation, they have to believe what the priest and bible says, as much to the chagrin of priests/bishops/pastors/etc the world over, angels, devils, gods and even Jesus tend not to drop in for a visit on demand.

Read the first paragraph, there are two different experiments described, only the second appears controversial.

quote:

Originally posted by wordsworm:I tried to play around with differing speeds of orbited object until I got to any orbited neutron which has an orbiting electron. If that atom moved at even half the speed of light, it would render any orbit at all impossible if gravitational effect moved merely at the speed of light.

I hesitate to ask, but why? At what speed does it become possible?

quote:

I didn't miss the point of special relativity. I was disagreeing with it. And a sound wave doesn't change speed according to the object making the sound. It remains constant no matter how you're moving. If, on the other hand, the medium itself is moving, as in the air in the cabin of an airplane, it changes everything.

For your air in cabin example, change your frame of reference to the cabin, and you find that nothing is moving. Light is measured at the same speed in all frames of reference.

Nice article. But like I said in a previous post, sound has similarities that are not entirely followed through with. That is to say, sound travels at a constant speed, regardless of the movement of the object. You can travel 100km/h and the sound that you make will remain the same. If you travel at 1,000km/h, you can shout to the guy in front of you and he'll never hear you. But, if you put yourselves in a cabin, say like in an air plane, he'll hear you just fine. If you could somehow 'see' the sound wave from the ground (stationary position, naturally), you would see it travel at +/- the speed of sound + 1,000km/h. I suspect that light would do the same. Although, I'm not entirely sure what substance causes the wave pattern in light, whereas we know that air causes the wave, or bubble as I read recently it being described as, in sound. We all know that light will behave differently, and travel more slowly, in water as it does in a vacuum. Nonetheless, were a cabin capable constructed and the speed of the light measured, I'm certain we'd see the same effect we do with sound as we do with light.

In the first case I take you to mean you are travelling at 100km/h relative to the bulk motion of the air around you? If so then the pressure waves your vocal chords create will move out from your body at (speed_of_sound - 100km/h) forward of your motion and (speed_of_sound + 100km/h) rearward in your reference frame (the one where you are not moving). This is also the case for the 1000km/h case you mention (with the obvious substitution) however if you go a bit faster relative to the air then you will exceed the local speed of sound, which at room 20C is ~12000km/h, and indeed in that case the guy ahead of your travel will not hear you before you hit him. The speed of a displacement wave is determined by the speed of motion of the air molecules banging into each other and transmitting the information of the sound disturbance in a chain reaction. That particle speed depends on temperature only. Obviously in the sealed aircraft you are stationary to the bulk motion of the air so it is entirely equivalent to you being on the ground and in an 0km/h wind, everything happening outside the aircraft is irrelevant (the equivalence theory that hold up nicely to fractions of speed of light).

You would not see the same effect with light as you do with sound as it has been proven experimentally numerous times that there is no ether in which it propagates so you may not draw a meaningful analogy between the longitudinal mechanical waves in matter and the EM transverse wave of light, there is no logicl reason why they should act similarly really. For example see http://en.wikipedia.org/wiki/M...%93Morley_experiment .

Popper was largely correct. For a revolutionary theory to win the public's trust, it needs to predict something surprising, and be correct. Einstein happened to be right despite the questionable verification of his theory via eclipse data. This was far from enough to vindicate his theory. He won the Nobel not for relativity but for Brownian motion. It was decades later that relativity was finally canon, having survived many tests by then.

An important fact about things like relativity, Maxwell's equations, is the sociological impact. There is little reason for the lay person to be skeptical of relativity. If scientists tell him the universe works a certain way on a grand scale, he'd be inclined to accept it.

Politically relevant theories are just going to have to withstand a higher level of scrutiny. People are more skeptical of that which demands a change in their most cherished beliefs or way of life. The heliocentric model took centuries to catch on due to political resistance. This is why things like evolution and AGW face such skepticism from the public at large.

And I'd have to say both theories fail at producing "surprising truths". "Surprising" in that it could not have been reasonably predicted outside the theory, "truth" as in something no one can deny (such as a chemical glowing a certain color under flame).

Popper himself once said that evolution wasn't really a scientific theory (later he retracted). I'm inclined to be skeptical of evolution myself, but seeing as the only offered alternatives are metaphysically bankrupt, I'll keep believing in evolution.

Climate change fails in both generating surprising, undeniable truths (most scientific theories), and in having a paucity of alternative competing theories (evolution's out). And if true, it demands we change our way of life. That is why there is so much contention about AGW.

Originally posted by wordsworm:GPS systems need constant corrections in order for them to function. If we'd absolutely figured all this stuff out we'd not have to do that. That is to say, since we have the calculations for them to remain above in the starry heaven, then why do they need constant corrections? No, that's not the case. The calculations you see are averages, not constants.

If only life would be that simple. Earth's gravitational field is not spherically symmetric. Fine, say we account for that - enough data will provide a reasonably good potential map. Then the Moon is introducing perturbations - well, we map the field of the Moon and we know how it moves around the Earth, so we can predict things again, right? wrong - the Sun perturbs the Moon's trajectory. And so on.

In fact, you can easily see a problem already at the Earth-Moon-satellite system. General 3-body systems have no analytical solution for the equations of motion. Sure, the satelite mass is very small, so you can do perturbation analysis - as you can do for the Sun-Earth-Moon system. But errors will accumulate. So you need to adjust your constants from time to time to account for that.

Bottom line - knowing the equations is not the same as knowing the solution. Having the GR equations for the sattelite + Earth + Moon + Sun system is not the same as having the functional form of the satellite's trajectory as a function of time. If it were, Math would be a lot more boring.

Originally posted by grstanford:Fortunately, the classroom students are (potentially if the teacher/school system allows) able to put the science teachings to the test in the form of experiments and see for themselves if what is being said is true.

Unfortunately for the priests congregation, they have to believe what the priest and bible says, as much to the chagrin of priests/bishops/pastors/etc the world over, angels, devils, gods and even Jesus tend not to drop in for a visit on demand.

You are wrong in your assessment of the congregation. They very much are free to put to the test what the pastor/priest/church tells them. They run it through their filter much like any other information they receive from other sources and reach a conclusion. If they agree, they might stay in that congregation. If they disagree, they will most likely move on or not go to church at all. There are millions of pro-choice Catholics that make your statement rediculous.

The original poster stated it correctly. Whether you like it or not, its pretty much the same model.

No, an experiment can be physically performed for all present to see and verify and replicate.

No running through mental filters required. Either the experiment did what the theory/law said it would or it didn't.

The congregation can filter the priests words or the bible or whatever for the rest of their lives if they so desire, and I can guarantee they won't get any visitations from god, angels, demons or whatever (except in their deranged imaginings).

How about people try talking about science without reference to religion for a change?

Well, I for one would welcome that, you will note, that it was not I who brought religion into this thread, and I don't understand why it was, except that certain religious conservative types (the types that got Bush into the white house and fuel the conservative political religious right wing) appear to be hell bent on discrediting science at every available opportunity and holding up religion as a credible alternative.

One has to wonder if this is what causes societies to eventually collapse.

Originally posted by Soulrift:There are far too many similarities between a congregation nodding obediently as a preacher tells them what to believe about God and a classroom nodding obediently as a teacher tells them what to believe about Science.

The difference being, of course, that if someone wants to replicate scientific experiments they can actually observe the evidence for scientific theories. Good luck replicating the resurrection or any other religious claim.